Bullous pemphigoid is an acquired autoimmune dermatitis, in which mast cells have been implicated as important effector cells. Like the physical allergies and mastocytoses, bullous pemphigoid provides a unique setting for assessing the contribution of mast cells to the pathophysiologic events of an immunologically-mediated disease. To achieve these goals, we plan to biopsy lesions in patients with bullous pemphigoid. In the tissues we will determine mast cell distribution and how mast cell phenotype and/or degranulation-regranulation characteristics correlate with stage of lesion development, associated lymphocytes, associated eosinophils, and state of endothelial activation. The findings will provide insight into the specific role of mast cells in mediating the pathophysiologic events. Controls will include mast cells in normal tissues and clinically similar dermatitides. Findings will be quantitated and apparent differences tested for statistical significance.